1. Field of the Invention
The present invention relates generally to mobile spectrometers and, more particularly, to an apparatus for the fast, precise, non-destructive testing of metals.
2. The Prior Art
Apparatus for the spectrometric analysis of the chemical composition of metallic parts, have been known for some time. In a known apparatus of this type, a plurality of spacing supports are located adjacent a vaporizing device, formed as a spark electrode, holding the spark electrode at a fixed distance from the part when positioned on the part. The radiation emitted by the metal vapor brought to luminescence by the device is transmitted to a spectroscope by a flexible optical waveguide. The waveguide is fastened to the base of a probe and its free end constitutes the sensing head which is pointed towards the plasma of the luminous metal vapor. The spectroscope is housed in a mobile unit, that also contains the energy source for the vaporizing device (see German Pat. No. 2,626,233).
It has been learned that external factors affect the operation and the range of application of such an apparatus. Specifically, factors which impair the stability of a plasma, such as the stability of a spark or of an arc, and factors which affect the transmission of the radiation from the luminous metal vapor to the sensing head, affect the operation and the range of application of such an apparatus. Thus the stability of the spark is impaired by uncontrollable air currents which can not be completely eliminated by the location of the spark electrode in a chamber alone. The transmission of the radiation is attenuated when passing through air. The attenuation depends on the wavelength of the light and increases as the wavelength becomes shorter. This known manually-operated apparatus is accordingly suitable only for the determination of components with long wavelengths. The analytical determination of components which produce radiation of short wavelengths are, therefore, usually accomplished in a laboratory with stationary equipment. In the laboratory, a sample of the part to be analyzed is studied in a protective gas atmosphere, such as an argon whereby wavelengths below 250 nm can also be determined.
Another disadvantage of this known apparatus resides in that a portion of the vaporized material itself settles on the sensing head which reduces the collection of radiation. The sensing head, therefore, must be cleaned periodically.
Besides apparatus of this kind, equipment also is known in which the spectrometric analytical apparatus is acommodated in a portable cabinet, housing the vaporizing device. A sleevelike chamber, open on one end, surrounds the device and serves as a spacing support. This apparatus is however unwieldy and requires great physical effort for handling by an operator (see the German Pat. Nos. 2,513,345 and 2,513,358). A device also is known in which an opening is provided in the rear of the electrode chamber through which gases formed are allowed to escape (see the British Pat. No. 1,444,255).
A portable apparatus for the spectrometric analysis of the chemical composition of flat metallic parts also is known, see the recently granted U.S. Pat. No. 4,411,524. As disclosed herein, a protective gas, preferably argon, is continuously admitted into the vicinity of the vaporizing portion and of the sensing head thereof so as to continuously flush both the spark electrode and the sensing head. This protective gas also enables the sensing of short-wave radiation, particularly that emitted by carbon, in the wavelength region below 250 nm by enhancing the intensity of its spectral line emission. This apparatus also features a ringlike nozzle about the spark electrode so as to direct a coolant airflow via a fan, with the counter electrode supported by a heat sink. In addition to the above features designed to stabilize the spark in the analytical gap, further stabilization of the spark is aided by the provision of a screen, preferably of boron nitride, to facilitate the controlled flushing of the flat metal surface being analyzed by the protective argon gas.
Extensive field experience has disclosed that the above apparatus, while satisfactory for most applications, has failed to provide that degree of precision reading, particularly as regards carbon content, as required to eliminate expensive sorting errors in the mill or in the yard. Part of this problem has been traced to the presence of objectionable matter on the surface of the metallic part, such as rust or the like. It has also been noted that the presence of an auxiliary spark gap in the pulse generator further destabilized the apparatus, again adversely affecting readings. Such auxiliary spark gaps are inherently unstable, requiring frequent adjustments and cleaning. Additionally, auxiliary spark gaps remain sensitive to atmospheric conditions, such as moisture and temperature, which adversely affect the use of analytical apparatus incorporating such pulse generators. Further, the above apparatus per U.S. Pat. No. 4,411,524 is limited to analyzing flat metallic parts only. It cannot properly be used to sort and analyze round metallic parts, such as welding wire or the like.